Successive-Approximation-Register (SAR) analog-to-digital converters (ADC) are widely used in many applications. A SAR ADC converts an analog input signal into a digital output data and comprises a SAR controller for successive approximation and a DAC (digital-to-analog converter) for converting a digital code into a voltage. It is difficult to make a high resolution conversion for an SAR ADC, because doing so generally requires using a high resolution DAC. This typically requires more steps of successive approximation for updating the digital code and therefore limits the conversion speed of SAR ADC, as it takes longer to finish the successive approximation. In brief, it is difficult to achieve both high resolution conversion and high conversion speed in a given device.
Accordingly, it is desired to provide an apparatus and method providing a SAR ADC with an acceptable balance between conversion speed and resolution